352 THE MICROSCOPE. 



tinguishable, two nuclei may frequently be found in each 

 semicircular division. These nuclei may he readily ex- 

 tracted from the containing grain by pressure, and after 

 separation retain their original form. In the next stage, 

 the greater number of grains consist of the semicircular 

 divisions, naturally separated, but now containing only 

 one nucleus, which has gradually increased in size. In 

 the succeeding stage the grain apparently consists of the 

 nucleus of the former stage, but considerably enlarged, 

 and having an oval form, and a somewhat granular surface. 

 This oval grain, continuing to increase in size, and in the 

 thickening of its membrane, acquires a pale yellow colour; 

 and is now the perfect grain pollen." 



In the whole tribe of Orchideae an abundance of raphides 

 may be found in almost every part of the cellular tissue. 

 The crystals are usually cylindrical in form, and so arranged 

 as to disguise their true character, often causing them to 

 be overlooked : by making use of a dark-ground illumina- 

 tor, or polarised light, this is not likely to occur. The 

 cause of the disease known as " spot " in Orchids, of 

 which several kinds have been noticed by cultivators, has 

 been traced by Mr. Berkeley, in one instance, to the oc- 

 currence of a minute parasitic fungus, belonging to the 

 genus Leptothyrium. A description of the disease, with 

 illustrations, giving the general appearance of the diseased 

 leaves, and a magnified figure of the parasite, appears in 

 the 1st part of the new series of the Journal of the Horti- 

 cultural Society. 



The Colouring matter of Flowers. — M. F. Hildebrands, 

 having carefully investigated the colouring matters of 

 flowers, has arrived at the following conclusion respecting 

 them, and their distribution in the tissue of the several 

 organs. 



1. That the colour of flowers is in constant connexion 

 with the cell contents, never with the walls of cells. 



2. Blue, violet, rose, and (if there be no yellow in the 

 flower) deep red are due, with little exception, to a cell- 

 fluid of corresponding colour. 



3. Yellow, orange, and green, are usually associated 

 with solid, granular, or vesicular substances in the 

 cells. 



